Injection molded thermoplastic starch/natural rubber/clay nanocomposites: Morphology and mechanical properties

Unmodified and modified natural rubber latex (uNRL and mNRL) were used to prepare thermoplastic starch/natural rubber/montmorillonite type clay (TPS/NR/Na⁺-MMT) nanocomposites by twin-screw extrusion. After being dried, the nanocomposites were injection molded to produce test specimens. Scanning electron micrographs of fractured samples revealed that chemical modification of NRL enhanced the interfacial adhesion between NR and TPS; improving their dispersion. X-ray diffraction (XRD) showed that the nanocomposites exhibited partially intercalated/exfoliated structures. Surprisingly, transmission electron microscopy (TEM) showed that clay nanoparticles were preferentially intercalated into the rubber phase. Elastic modulus and tensile strength of TPS/NR blends were dramatically improved from 1.5 to 43 MPa and from 0.03 to 1.5 MPa, respectively, as a result of rubber modification. Properties of blends were almost unaffected by the dispersion of the clay except for the TPS/mNR blend loading 2% MMT. This was attributed to the exfoliation of the MMT.     

Preparation and adsorption behavior for brilliant blue X-BR of the cost-effective cationic starch intercalated clay composite matrix

In order to increase the adsorption capacity of cationic starch and avoid the loss of cationic groups, novel and cost-effective cationic starch (CS) intercalated clay composite matrix was prepared by controlling the weight ratio of clay and CS. Intercalated microstructure of the composite matrix was characterized by FTIR and XRD, respectively. Reactive dye (brilliant blue X-BR) was used to study adsorption behaviors of the matrix under various parameters such as weight ratio of clay to CS, initial dye concentration, contact time and temperature. Adsorption equilibrium, thermodynamics and kinetics models were further investigated. The results showed that the adsorption capacity increased greatly with increasing the weight ratio of clay to CS from 0.1 to 0.2, and then decreased when the weight ratio up to 0.3. The adsorption isotherm fitted well with the Langmuir isotherm model with a maximum adsorption capacity of 122.0 mg/g. Kinetic study showed that the pseudo-second-order model provided a better correlation of experimental data. Furthermore, the thermodynamic parameters were also calculated.     

Thermal properties and flammability of polylactide nanocomposites with aluminum trihydrate and organoclay

Biodegradable polylactide (PLA) nanocomposites with aluminum trihydrate (ATH) and modified montmorillonite (MMT) were prepared via direct melt compounding using a twin-screw micro extruder. The exfoliated and intercalated structures of clay in the matrix were observed by TEM and XRD. The thermal oxidative degradation temperature and activation energy of the PLA/ATH/MMT nanocomposite determined by thermogravimetric analysis are higher than that without addition of ATH and organoclay. The incorporation of layered silicates into the PLA/ATH composite results in further stabilization throughout the degradation step. The V-0 rating (UL94 V) of the PLA nanocomposite has been achieved, and the melt dripping was reduced during combustion. Results showed that high loading of the conventional flame retardant ATH yielded brittle PLA composites; however, replacing a portion of the ATH with modified MMT in the PLA matrix improved this result.     

Properties of biodegradable citric acid-modified granular starch/thermoplastic pea starch composites

Pea starch-based composites reinforced with citric acid-modified pea starch (CAPS) and citric acid-modified rice starch (CARS), respectively, were prepared by screw extrusion. The effects of granular CAPS and CARS on the morphology, thermal stability, dynamic mechanical thermal analysis, the relationship between the mechanical properties and water content, as well as the water vapor permeability of the composite films were investigated. Scanning electron microscope and X-ray diffraction reveal that the reinforcing agents, the granules of CAPS and CARS, are not disrupted in the thermoplastic process, while the pea starch in the matrix is turned into a continuous TPS phase. Granular CAPS and CARS can improve the storage modulus, the glass transition temperature, the tensile strength and the water vapor barrier, but decrease thermal stability. CARS/TPS composites exhibit a better storage modulus, tensile strength, elongation at break and water vapor barrier than CAPS/TPS composites because of the smaller size of the CARS granules.     

In vitro assessment of the enzymatic degradation of several starch based biomaterials

The susceptibility of starch-based biomaterials to enzymatic degradation by amylolytic enzymes (glucoamylase and alpha-amylase) was investigated by means of incubating the materials with a buffer solution, containing enzymes at different concentrations and combinations, at 37 degrees C for 6 weeks. Two polymeric blends of corn starch with poly(ethylene-vinyl alcohol) copolymer and poly(epsilon-caprolactone), designated by SEVA-C and SPCL, respectively, were studied. The material degradation was characterized by gravimetry measurements, tensile mechanical testing, scanning electron microscopy (SEM), and Fourrier transform infrared-attenuated total reflectance (FTIR-ATR). The degradation liquors were analyzed for determination of reducing sugars, as a result of enzyme activity, and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to identify the degradation products. All of the analysis performed showed that starch polymeric blends are susceptible to enzymatic degradation, as detected by increased weight loss and reducing sugars in solution. alpha-Amylase caused significant changes on the overall mechanical properties of the materials, with a decrease of about 65% and 58% being observed in the moduli for SEVA-C and SPCL, respectively, when compared with the control (samples incubated in buffer only). SEM analysis detected the presence of fractures and pores at the material's surface as a result of starch degradation by amylolytic enzymes. FTIR spectra confirmed a decrease on the band corresponding to glycosidic linkage (-C-O-C-) of starch after incubation of the materials with alpha-amylase. In contrast, the incubation of the polymers in buffer only, did not cause significant changes on the material's properties and morphology. Comparing the two materials, SEVA-C exhibited a higher degradability, which is related to the physicochemical structure of the materials and also to the fact that the starch concentration is higher in SEVA-C. The identification of the degradation products by HPAEC-PAD revealed that glucose was the major product of the enzymatic degradation of starch-based polymers. alpha-Amylase, as expected, is the key enzyme involved in the starch degradation, contributing to major changes on the physicochemical properties of the materials. Nevertheless, it was also found that starch-based polymers can also be degraded by other amylolytic enzymes but in a smaller extent.     

Effect of citric acid and processing on the performance of thermoplastic starch/montmorillonite nanocomposites

A facile two steps extrusion processing conditions are used to prepare thermoplastic starch (TPS)/glycerol modified-montmorillonite (GMMT) nanocomposites. X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrate glycerol can enlarge the d-spacing and destruct the multilayer structure of montmorillonite (MMT) effectively using high speed emulsifying machine (HSEM) in the first modification step. So the enlarged d-spacing and destructed platelets of MMT are favorable to form intercalated or exfoliated TPS/GMMT nanocomposites in the second melt extrusion processing. However, scanning electron microscopy (SEM) and XRD show the possible competition between TPS matrix and plasticizer for the intercalation between MMT layers can deteriorate the plasticization of TPS. In addition, citric acid (CA) can increase the plasticization of TPS and dispersion of MMT in nanocomposites effectively detected by fourier transform infrared (FT-IR) spectroscopy and SEM. At the same time, this facile processing conditions and CA can improve the mechanical properties and water vapor permeability (WVP) of TPS/GMMT nanocomposites obviously.     

Morphological and thermal properties of cellulose-montmorillonite nanocomposites

Cellulose-layered montmorillonite (MMT) nanocomposites were prepared by precipitation from N-methylmorpholine- N-oxide (NMMO)/water solutions. Two hybrid samples were obtained to investigate the influence of the reaction time on the extent of clay dispersion within the matrix. It was observed that longer contact times are needed to yield nanocomposites with a partially exfoliated morphology. The thermal and thermal oxidative properties of the hybrids, which might be of interest for fire-resistant final products, were investigated by thermogravimetry and chemiluminescence (CL). The nanocomposites exhibited increased degradation temperatures compared to plain cellulose, and the partially exfoliated sample showed the maximum stability. This result was explained in terms of hindered transfer of heat, oxygen, and degraded volatiles due to the homogeneously dispersed clay filler. Kinetic analysis of the decomposition process showed that the degradation of regenerated cellulose and cellulose-based hybrids occurred through a multistep mechanism. Moreover, the presence of nanoclay led to drastic changes in the dependence of the activation energy on the degree of degradation. CL analysis showed that longer permanence in NMMO/water solutions brought about the formation of carbonyl compounds on the polymer backbone. Moreover, MMT increased the rate of dehydration and oxidation of cellulose functional moieties. As a consequence, cellulose was found to be less stable at temperatures lower than 100 degrees C. Conversely, at higher temperatures, the hindering of oxygen transfer prevailed, determining an increase in thermo-oxidative stability.     

Butane 2,3-diol production by immobilizedAeromonas hydrophila

A technique for immobilizing cells ofAeromonas hydrophila on a titanium (IV) hydroxide matrix was developed. Immobilized cells were used to produce butane 2,3-diol from soluble starch. The influence of the addition of 1 g/l sodium acetate to the starch-based medium on diol production depended on the initial starch: acetate ratic.     

Direct electron transfer of hemoglobin in layered alpha-zirconium phosphate with a high thermal stability

A heme protein hemoglobin (Hb) was reacted with preexfoliated layered alpha-zirconium phosphate (alpha-ZrP) platelets. An X-ray diffraction (XRD) pattern of small range showed that the exfoliated alpha-ZrP platelets reassembled after the addition of Hb molecules, with the protein intercalated between the layers. UV-Vis and Fourier transform infrared (FTIR) spectra analysis displayed that no significant denaturation occurred to the intercalated protein. The bioactivity of Hb was also investigated by testing the electrochemical properties of the Hb/alpha-ZrP composite. Results showed that the intercalation of Hb into the layered material not only improved the thermal stability of Hb but also enhanced the direct electron transfer ability between protein molecules and electrode. The protein still showed bioactivity after treatment at a temperature as high as 85 degrees C. A pair of well-defined redox peaks at approximately -0.37 and -0.32V was observed on the cyclic voltammograms (CVs) of the Hb/alpha-ZrP composite modified electrode, and the electrode reactions showed a surface-controlled process with a single proton transfer. The resultant biosensor constructed by the Hb/alpha-ZrP composite displayed an excellent response to the reduction of hydrogen peroxide (H(2)O(2)) with good reproducibility.     

Nano clay reinforced PCL/starch blends obtained by high energy ball milling

Sodium montmorillonite was incorporated into a poly(ε-caprolactone)–starch blend by means of a ball mill. The structural organization and physical (mechanical, thermal and barrier) properties were analyzed and correlated with the milling conditions. Scanning electron microscopy and X-ray characterization show that the milling process can improve the compatibilization between the PCL and the starch phases, while promotes the dispersion of clay minerals at nanometric level. The milling time strongly influences the mechanical and barrier properties. In particular, the best results in terms of elastic modulus and permeability coefficient were achieved with a complete delamination of the pristine clay structure. In summary, the milling process not only has demonstrated to be a promising compatibilization method for immiscible PCL–starch blends, but it can be also used to improve the dispersion of nanoparticles into the polymer blends.     

Interaction and properties of highly exfoliated soy protein/montmorillonite nanocomposites

The soy protein isolate (SPI)/ Na+ -montmorillonite (MMT) plastics were successfully prepared, and their structures and properties were characterized with X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and tensile testing. The interactions between the soy protein macromolecules and MMT in aqueous media were analyzed with zeta-potential measurements, Fourier transform infrared spectroscopy, and electrostatic surface potential calculations. The results revealed that the heterogeneous distribution of the surface positive charges provided the positive-charge-rich domains for the soy globulins bearing net negative charges to anchor into the negatively charged MMT galleries. There were electrostatic attraction and hydrogen bonding interactions on the interfaces of the soy protein and MMT, which led to the good dispersion of the phyllosilicate layers in the protein matrix. The highly exfoliated MMT layers with a dimension of 1-2 nm in thickness were randomly dispersed in the protein matrix containing MMT lower than 12 wt %, whereas the intercalated structure was predominant when the MMT content was higher than 12 wt %. Consequently, the fine dispersion of the MMT layers and the strong interactions between SPI and MMT created the significant improvement of the mechanical strength and thermo-stability of the SPI/MMT plastics. In addition, a schematic illustration was proposed to describe the electrostatic interaction between SPI and MMT as well as the correlation between the interaction and structure in protein/clay systems.     

Starch graft poly(methyl acrylate) loose-fill foam: preparation, properties and degradation

Starch graft poly(methyl acrylate) (S-g-PMA) was prepared by ceric ion initiation of methyl acrylate in an aqueous corn starch slurry (prime starch) which maximized the accessibility of the starch for graft polymerization. A new ceric ion reaction sequence was established as starch-initiator-methyl acrylate followed by addition of a small amount of ceric ion solution when the graft polymerization was almost complete to quench the reaction. As a result of this improved procedure, no unreacted methyl acrylate monomer remained, and thus, essentially no ungrafted poly(methyl acrylate) homopolymer was formed in the final grafted product. Quantities of the high purity S-g-PMA so prepared in pilot scale were converted to resin pellets and loose-fill foam by single screw and twin screw extrusion. The use of prime starch significantly improved the physical properties of the final loose-fill foam, in comparison to foam produced from regular dry corn starch. The S-g-PMA loose-fill foam had compressive strength and resiliency comparable to expanded polystyrene but higher bulk density. The S-g-PMA loose-fill foam also had better moisture and water resistance than other competitive starch-based materials. Studies indicated that the starch portion in S-g-PMA loose-fill foam biodegraded rapidly, whereas poly(methyl acrylate) remained relatively stable under natural environmental conditions.     

Structural characterization and properties of starch/konjac glucomannan blend films

In this work, a series of glycerol-plasticized pea starch/konjac glucomannan (ST/KGM) blend films was prepared by a casting and solvent evaporation method. The structure, thermal behavior, and mechanical properties of the films were investigated by means of Fourier Transform Infrared Spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and tensile testing. The results indicated that strong hydrogen bonding formed between macromolecules of starch (ST) and konjac glucomannan (KGM), resulting in a good miscibility between ST and KGM in the blends. Compared with the neat ST, the tensile strength of the blend films were enhanced significantly from 7.4 to 68.1 MPa with an increase of KGM content from 0 to 70 wt%. The value of elongation at break of the blend films was higher than that of ST and reached a maximum value of 59.0% when the KGM content was 70 wt% and 20% of glycerol as plasticizer. The incorporation of KGM into the ST matrix also led to an increase of moisture uptake for the ST-based materials. The structure and properties of pea starch-based films were modified and improved by blending with KGM.     

Optimization of cyclodextrin glycosyltransferase production from Klebsiella pneumoniae AS-22 in batch, fed-batch, and continuous cultures

Production of a novel cyclodextrin glycosyltransferase (CGTase) from Klebsiella pneumoniae AS-22 strain, which converts starch predominantly to alpha-CD at high conversion yields, in batch, fed-batch, and continuous cultures, is presented. In batch fermentations, optimization of different operating parameters such as temperature, pH, agitation speed, and carbon-source concentration resulted in more than 6-fold increase in CGTase activity. The enzyme production was further improved by two fed-batch approaches. First, using glucose-based feed to increase cell density, followed by starch-based feed to induce enzyme production, resulted in high cell density of 76 g dry cell weight/L, although the CGTase production was low. Using the second approach of a single dextrin-based feed, 20-fold higher CGTase was produced compared to that in batch fermentations with media containing tapioca starch. In continuous operation, more than 8-fold increase in volumetric CGTase productivity was obtained using dextrin-based media compared to that in batch culture using starch-based media.     

Application of biodegradable natural polymers for flocculated sedimentation of clay slurry

Tamarind seed kernel powder (TSKP) is a cheap starchy biodegradable material that has not been tested before for its flocculating properties. Sedimentation of clay slurry has been studied using this material. We have also done experiments with chemical grade starch and its blends with TSKP and compared their performance with that of potash alum for sedimentation of the clay slurry. The sedimentation phenomenon showed constant and falling rate zones. Sedimentation velocity, mass flux and concentration have been calculated at different time intervals for all the flocculants. Among the three types of natural flocculants, starch showed the highest rate constant in the constant rate zone and TSKP offers faster sedimentation in the falling rate zone. Thus TSKP, starch and their blends are potentially attractive environmentally benign flocculants. A qualitative explanation of the flocculating property of TSKP has been given.     

Preparation and characterization of glycerol plasticized-pea starch/ZnO–carboxymethylcellulose sodium nanocomposites

Among natural polymers, starch is one of the most promising biodegradable materials because it is a renewable bioresource that is universally available and of low cost. However, the properties of starch-based materials are not satisfactory. One approach is the use of nano-filler as reinforcement for starch-based materials. In this paper, a nanocomposite is prepared using ZnO nanoparticles stabilized by carboxymethylcellulose sodium (CMC) as the filler in glycerol plasticized-pea starch (GPS) matrix by the casting process. According to the characterization of ZnO–CMC particles with Fourier transform infrared (FTIR), Ultraviolet–visible (UV–vis), X-ray diffraction (XRD), transmission electron microscope (TEM) and thermogravimetric analysis (TG), ZnO (about 60 wt%) is encapsulated with CMC (about 40 wt%) in ZnO–CMC particles with the size of about 30–40 nm. A low loading of ZnO–CMC particles can obviously improve the pasting viscosity, storage modulus, the glass transition temperature and UV absorbance of GPS/ZnO–CMC nanocomposites. When the ZnO–CMC contents vary from 0 to 5 wt%, the tensile yield strength increase from 3.94 MPa to 9.81 MPa, while the elongation at break reduce from 42.2% to 25.8%. The water vapor permeability decrease from 4.76 × 10⁻¹⁰ to 1.65 × 10⁻¹⁰ g m⁻¹ s⁻¹ Pa⁻¹.     

A new amphoteric superabsorbent hydrogel based on sodium starch sulfate

A new amphoteric superabsorbent hydrogels were synthesized by graft copolymerization blending based on acrylamide (AM), diallydimethylammonium chloride (DMDAAC) and sodium starch sulfate (SSS). The effect of polymerization conditions on swelling capacity was investigated. The results showed that the swelling capacity was affected by various factors, such as polymerization temperature, concentration of initiator and crosslinker, and dose of AM. Additionally, the results testified that salt bond was a potential crosslinking factor in the amphoteric hydrogel. The maximum swelling capacity in distilled water and saline solution reached 1493.1 and 91.0 g/g, respectively. These results were compared with those obtained from original starch-based hydrogel.     

Injection-molded nanocomposites and materials based on wheat gluten

This is, to our knowledge, the first study of the injection molding of materials where wheat gluten (WG) is the main component. In addition to a plasticizer (glycerol), 5 wt.% natural montmorillonite clay was added. X-ray indicated intercalated clay and transmission electron microscopy indicated locally good clay platelet dispersion. Prior to feeding into the injection molder, the material was first compression molded into plates and pelletized. The filling of the circular mold via the central gate was characterized by a divergent flow yielding, in general, a stronger and stiffer material in the circumferential direction. It was observed that 20-30 wt.% glycerol yielded the best combination of processability and mechanical properties. The clay yielded improved processability, plate homogeneity and tensile stiffness. IR spectroscopy and protein solubility indicated that the injection molding process yielded a highly aggregated structure. The overall conclusion was that injection molding is a very promising method for producing WG objects.     

Optimization of conditions for production of sago starch-based foam

Production of sago starch-based foam involved mixing of sago starch with polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP) followed by preparation of electron beam irradiated sago starch/PVA and sago starch/PVP sheets and expanding them in a microwave. The results revealed that good foams with high linear expansion and closed cell structure can be produced from 25:15 of sago starch:PVA and 30:10 of sago starch:PVA blends prepared at 80 °C and electron beam irradiated at 15 kGy or 10 kGy for the cross-linking process. An increment of sago starch in the blends enhanced the linear expansion of the foams produced. Change in the blend morphology was observed when it was exposed to higher irradiation doses as electron beam irradiation induced the cross-linking in PVA and PVP, and leaching of amylose and amylopectin from the starch granules. Sago starch/PVA blend is more suitable for foam production because it produced flexible and glossy foam as compared to sago starch/PVP blend which produced very rigid foam.     

Thermoplastic corn starch/clay hybrids: Effect of clay type and content on physical properties

Thermoplastic corn starch (TPS) hybrids, plasticized with glycerol and reinforced with two types of clay (sodium montmorillonite and Cloisite^® 30B), were prepared by melt-extrusion. Scanning electron microscopy was used to visualize extrudates morphology. The effects of clay content and of glycerol content on the physical properties of extrudates were evaluated. As determined by contact angle measurements and X-ray diffraction, the increase in glycerol content led to materials with higher hydrophilicity, and higher B-type crystallinity. Addition of clay resulted in hybrid materials with improved properties in relation to TPS alone, even after conditioning at a high relative humidity for 90 days. X-ray diffraction was also used to evaluate clay intercalation within the polymeric matrix, before and after conditioning. Soil burial biodegradation tests, carried out for TPS alone and for TPS/Cloisite 30B hybrids, and followed by weight loss measurements, revealed that biodegradation was enhanced for the hybrid materials in comparison with TPS.